The present invention relates to a device for measuring the value of a parameter relating to an electrically conductive object. Such a parameter can be the electric conductivity or the degree in which the material has changed under the influence of external conditions. Alternatively the parameter is the quality of a weld or the thickness of the object.
International patent application No. 98/02 714, hereby incorporated by reference, relates to measuring the wall thickness of an electrically conductive object. During normal operation, a pulsed eddy current is induced in the object, the decay of the eddy current is determined and a signal is produced representing the decay. The wall thickness can be determined from the signal representing the decay of the eddy current. The wall thickness is determined from the length of a time interval in which the signal decays from a first value to a second, lower, value. Determining the wall thickness involves a numerical operation.
U.S. Pat. No. 5,059,902, hereby incorporated by reference, discloses a device for measuring the value of a parameter relating to an electrically conductive object using a signal induced by decaying eddy currents in the object. The device comprises a transmitter coil, means for energizing the transmitter coil, a receiver coil having an output, a master clock, and a signal analysis unit, wherein the master clock controls the predetermined time during which the transmitter coil is energized and a second adjustable timer that controls the predetermined time during which the voltage is measured.
It would be advantageous to provide an alternative to the device known from U.S. Pat. No. 5,059,902, wherein the parameters relating to the electrically conductive object are measured with the method disclosed in International patent application, No. 98/02 714, wherein the result can be displayed on a display pertaining to the device, without the need for a numerical analysis.
In addition, it would be advantageous to provide a device that is so flexible that it can be used for such different activities as measuring the degree in which the material has changed under the influence of external conditions, determining the quality of a weld or measuring the thickness of the object.
The invention relates to a device for measuring a material property of an electrically conductive object and displaying a reading indicative of the material property on a display, which device comprises a transmitter coil, means for energizing the transmitter coil, a receiver coil having an output, a master clock, and a signal analysis unit comprising a hold-and-comparator unit and a digital counter, wherein the master clock comprises a first adjustable timer that controls the predetermined time during which the transmitter coil is energized, a second adjustable timer that controls the moment at which an initial value of the receiver coil signal is measured and held by the hold-and-comparator unit, and a third adjustable timer that controls the moment at which the digital counter starts, wherein the digital counter has a first input for a start-counting signal, a second input for a stop-counting signal and an output connected to the display, and wherein the hold-and-comparator unit has an input that is connected to the output of the receiver coil and an output that is connected to the second input of the digital counter, which hold-and-comparator unit outputs during normal operation a stop-counting signal if the value of the receiver coil signal is less than a scaled initial value of the receiver coil signal.